Problem: In history class, the girl to boy ratio is $7$ to $10$. If there are a total of $34$ students, how many boys are there?
Answer: A ratio of $7$ girls to $10$ boys means that a set of $17$ students will have $7$ girls and $10$ boys. A class of $34$ students has $2$ sets of $17$ students. Because we know that there are $10$ boys in each set of $17$ students, the class must have $2$ groups of $10$ boys each. There is a total of $20$ boys in history class.